support for flask app factory pattern

example/app.py

@@ -27,8 +27,8 @@
     },
 )
 
-db = MongoEngine(app)
-api = MongoRest(app)
+db = MongoEngine()
+api = MongoRest()
 
 class UserResource(Resource):
     document = documents.User
@@ -303,6 +303,8 @@ class DictDocView(ResourceView):
     resource = DictDocResource
     methods = [Fetch, List, Create, Update]
 
+db.init_app(app)
+api.init_app(app)
 
 if __name__ == "__main__":
     port = int(os.environ.get('PORT', 8000))

flask_mongorest/__init__.py

@@ -2,16 +2,64 @@
 from flask_mongorest.methods import Create, BulkUpdate, List
 
 
+class _DelayedApp(object):
+
+    '''
+    Stores URL rules for later merging with application URL map.
+
+    '''
+
+    def __init__(self):
+        self.url_rules = []
+
+    def add_url_rule(self, *args, **kwargs):
+        self.url_rules.append((args, kwargs))
+
+
 class MongoRest(object):
-    def __init__(self, app, **kwargs):
-        self.app = app
+
+    def __init__(self, app=None, **kwargs):
+        '''
+        Takes optional Flask application instance. If supplied, `init_app` will be
+        called to update application url map.
+
+        '''
+
         self.url_prefix = kwargs.pop('url_prefix', '')
-        app.register_blueprint(Blueprint(self.url_prefix, __name__, template_folder='templates'))
+        self.template_folder = kwargs.pop('template_folder', 'templates')
+        if app is not None:
+            self.init_app(app, **kwargs)
+        else:
+            self.app = _DelayedApp()
+
+    def init_app(self, app):
+        '''
+        Provides delayed application instance initialization to support
+        Flask application factory pattern. For further details on application
+        factories see:
+
+        http://flask.pocoo.org/docs/dev/patterns/appfactories/
+
+        and
+
+        http://mattupstate.com/python/2013/06/26/how-i-structure-my-flask-applications.html
+
+        '''
+        app.register_blueprint(
+            Blueprint(self.url_prefix,
+                      __name__,
+                      template_folder=self.template_folder))
+        if hasattr(self, 'app'):
+            if isinstance(self.app, _DelayedApp):
+                for args, kwargs in self.app.url_rules:
+                    app.add_url_rule(*args, **kwargs)
+        self.app = app
 
     def register(self, **kwargs):
         def decorator(klass):
 
-            # Construct a url based on a 'name' kwarg with a fallback to a Mongo document's name
+            # Construct a url based on a 'name' kwarg with a fallback to a
+            # Mongo document's name
             document_name = klass.resource.document.__name__.lower()
             name = kwargs.pop('name', document_name)
             url = kwargs.pop('url', '/%s/' % document_name)
@@ -24,11 +72,28 @@ def decorator(klass):
             pk_type = kwargs.pop('pk_type', 'string')
             view_func = klass.as_view(name)
             if List in klass.methods:
-                self.app.add_url_rule(url, defaults={'pk': None}, view_func=view_func, methods=[List.method], **kwargs)
+                self.app.add_url_rule(
+                    url,
+                    defaults={
+                        'pk': None},
+                    view_func=view_func,
+                    methods=[
+                        List.method],
+                    **kwargs)
             if Create in klass.methods or BulkUpdate in klass.methods:
-                self.app.add_url_rule(url, view_func=view_func, methods=[x.method for x in klass.methods if x in (Create, BulkUpdate)], **kwargs)
-            self.app.add_url_rule('%s<%s:%s>/' % (url, pk_type, 'pk'), view_func=view_func, methods=[x.method for x in klass.methods if x not in (List, BulkUpdate)], **kwargs)
+                self.app.add_url_rule(
+                    url,
+                    view_func=view_func,
+                    methods=[
+                        x.method for x in klass.methods if x in (
+                            Create,
+                            BulkUpdate)],
+                    **kwargs)
+            self.app.add_url_rule(
+                '%s<%s:%s>/' %
+                (url, pk_type, 'pk'), view_func=view_func, methods=[
+                    x.method for x in klass.methods if x not in (
+                        List, BulkUpdate)], **kwargs)
             return klass
 
         return decorator
-

flask_mongorest/views.py

@@ -56,6 +56,8 @@ def _dispatch_request(self, *args, **kwargs):
             return super(ResourceView, self).dispatch_request(*args, **kwargs)
         except mongoengine.queryset.DoesNotExist as e:
             return {'error': 'Empty query: ' + str(e)}, '404 Not Found'
+        except mongoengine.ValidationError as e:
+            return {'field-errors': e.errors}, '400 Bad Request'
         except ValidationError as e:
             return e.message, '400 Bad Request'
         except Unauthorized as e: